1. Field of the Invention
The present invention relates to a vacuum processing apparatus and a control method therefor.
2. Description of the Related Art
FIG. 10 shows the constitution of a typical conventional plasma etching apparatus 1 used for plasma etching. Referring to FIG. 10, the plasma etching apparatus 1 includes a processing chamber 2, which is installed in a clean room 8. A fluorocarbon type processing gas or the like is supplied into the processing chamber 2, and high-frequency electrical power is applied between electrodes, not shown, in the processing chamber 2, thus carrying out etching on a substrate to be processed in the processing chamber 2. In this way, in a semiconductor manufacturing process, semiconductor wafers are conveyed into the processing chamber, which is vacuable, and processing such as etching or film deposition is carried out in a vacuum atmosphere. An exhausting apparatus P that uses a turbo-molecular pump or the like as a vacuum pump is used in the vacuum processing.
The exhausting apparatus P is comprised of an automatic pressure regulator 4 that is connected to the bottom of the processing chamber 2 via an exhaust pipeline 3, a main vacuum pump 5 such as a turbo-molecular pump that is connected to the automatic pressure regulator 4, and an auxiliary vacuum pump 7 that is connected to the main vacuum pump 5 via piping 6. The processing chamber 2 is evacuated to a predetermined reduced pressure atmosphere by the pumps 5 and 7. The automatic pressure regulator 4, which is disposed on the intake port side of the main vacuum pump 5, has an opening/closing valve 28 such as a large-bore slide valve for regulating the pressure inside the processing chamber 2.
A controller, not shown, of the exhausting apparatus P monitors the value of the pressure inside the processing chamber 2, and controls the degree of opening of the opening/closing valve 28 based on this value, thus controlling the pressure inside the processing chamber 2.
The auxiliary vacuum pump 7 is connected in series with the main vacuum pump 5 on the discharge port side of the main vacuum pump 5. The auxiliary vacuum pump 7 puts the discharge port side of the main vacuum pump 5 into a vacuum state, whereby the main vacuum pump 5 can be made to operate efficiently. To maintain the exhausting performance of the main vacuum pump 5, in general it is necessary to set the discharge port (back pressure) side of the main vacuum pump 5 to less than approximately 133 Pa.
It is thus necessary to use a large pump of exhausting rate approximately 3000 L/min as the auxiliary vacuum pump 7 that is disposed downstream of the main vacuum pump 5. There has thus been a problem that large amounts of cooling water and driving energy are required for the auxiliary vacuum pump 7. In addition, problems have arisen such as it being necessary to specially provide a space separate to the clean room 8 such as a pump room for installing the auxiliary vacuum pump 7, and thus it being necessary to make the piping 6 that has large bore to obtain the desired conductance. Furthermore, because the piping 6 must have a large bore and be very long, the ability to carry out maintenance is poor, and there has been a risk of differences arising between different vacuum processing apparatuses such as differences in the conductance.
Moreover, according to the conventional plasma etching apparatus 1, the automatic pressure regulator 4 is disposed near to the processing chamber 2, and hence there has been a problem that particle that arises when controlling the degree of opening of the opening/closing valve 28 may get into the processing chamber 2; furthermore, a problem has arisen that, due to the necessity of matching the size of the opening/closing valve 28 to the flange size of the main vacuum pump 5, it is not possible to make the automatic pressure regulator 4 small, and hence the cost rises and moreover maintenance requires much time and labor.
Moreover, conventionally, the pressure inside the processing chamber 2 has been controlled purely by controlling the degree of opening of the opening/closing valve 28, not by controlling the rotational speeds of the main vacuum pump 5 and the auxiliary vacuum pump 7, and hence a problem has arisen that the scope for controlling the pressure inside the processing chamber 2 is narrow.